Random number generation in array

[Artyom]

Hi everybody!
Here's the problem:
I have an array of 4 integer elements and they must be initialized by random
numbers from 0 to 9 that shouldn't repeat. I tried many things, but some
elements (for example, first and third ones) continue repeating. Can you
propose an algorithm that solves this?
Thank you!

 

[lilburne]

Hi everybody!
Here's the problem:
I have an array of 4 integer elements and they must be initialized by random
numbers from 0 to 9 that shouldn't repeat. I tried many things, but some
elements (for example, first and third ones) continue repeating. Can you
propose an algorithm that solves this?
Thank you!

std::set<int> numbers;
while (numbers.size() <= 4) {
int random_int = get_random_integer();
numbers.insert(random_int);
}

// move values from set into array

 

[John Harrison]

Hi everybody!
Here's the problem:
I have an array of 4 integer elements and they must be initialized by random
numbers from 0 to 9 that shouldn't repeat. I tried many things, but some
elements (for example, first and third ones) continue repeating. Can you
propose an algorithm that solves this?
Thank you!

Fill an array (size 10) with numbers 0 to 9

Go though array randomly swapping each element with a later element (a
random shuffle)

Pick first four elements from randomly shuffled array.

john

 

[Miika Karanki]

std::set<int> numbers;
while (numbers.size() <= 4) {
int random_int = get_random_integer();
numbers.insert(random_int);
}

This could loop forever. What if get_random_integer() returns every time
the same number? It's still 'random'!

<http://www.sgi.com/tech/stl/random_shuffle.html> gives a nice STL solution
to the problem.

 

[Miika Karanki]

<http://www.sgi.com/tech/stl/random_shuffle.html> gives a nice STL solution
to the problem.

Sorry, it doesnt.

 

[David Harmon]

Sorry, it doesnt.

What's not to like about it?

int nums[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
std::random_shuffle(nums, nums+10);
std::copy(nums, nums+4, std:stream_iterator<int>(std::cout, " "));